1. Field of the Invention
The present invention relates to a scanning optical apparatus used in image recording apparatuses such as a laser printer, a digital copier, and the like that record an image on a photosensitive material by exposing the photosensitive material to a scanning laser beam in accordance with image information, and more particularly to a split scanning optical apparatus that splits and scans a surface to be scanned by plural light beams.
2. Description of the Prior Art
With advance in network technologies and advent of sophisticated computers, there has recently been a demand for image output of high speed and high resolution in image recording apparatuses such as a laser printer, a digital copier, and other output apparatuses. To achieve the requirements for high speed and high resolution, a technology not involving an increase in the number of rotations of a polygon mirror is proposed in Japanese Published Unexamined Patent Application Nos. Sho 54-128352 (hereinafter referred to as prior art 1) and Hei 6-255169 (hereinafter referred to as prior art 2). This technology relates to a split scanning optical apparatus that increases a substantial scanning speed without increasing the number of rotations of a polygon mirror by using plural light sources and forming one main scanning line with plural split scanning lines.
The above described split scanning optical apparatus has difficulty in accurately adjusting the position between split scanning lines to a desired position, and in order to obtain satisfactory output images, it must compensate for the timing of starting to output image information in accordance with the position between split scanning lines.
Output timing compensation is achieved, for a main scanning direction, by increasing or decreasing a delay amount from a horizontal synchronizing signal to the start of image information output, and for a sub scanning direction, by changing an image information output start timing in units of horizontal synchronizing signals in accordance with a positional deviation amount between split scanning lines in the sub scanning direction.
FIG. 10 shows a time chart on a deviation amount between split scanning lines in the sub scanning direction and the timing of image information output start.
As shown in FIG. 10, there is a positional deviation amount of three lines between split scanning lines A and B in the sub scanning direction. Accordingly, split image information A must be written a three-line period later than split image information B to match the position of image information on a photosensitive material in the sub scanning direction.
In the above described prior arts 1 and 2, mention is made of position compensation in the main scanning direction, but a positional deviation in the sub scanning direction is not taken into account.
Furthermore, in the split scanning optical apparatus, if there remained a small positional deviation of split scanning lines that cannot be compensated, images corresponding to joints of images formed by the split scanning lines would be disturbed. To prevent image quality from decreasing due to the disturbance, coincidence of image joint positions in the main scanning direction must be prevented by changing split image timing for every main scanning or joining split images in a position of image information corresponding to a light source off signal.
If such processing were performed by the split scanning optical apparatus in which a deviation of split scanning line position exists in the sub scanning direction, as shown in FIG. 10, pieces of image information to be written onto a photosensitive material during one-time main scanning would be written in different positions in the sub scanning direction by the split scanning lines. As a result, the split positions of the pieces of image information would be different.
Therefore, there exists a problem in that, to read out split image information, split position information must be delayed for a positional deviation of split scanning lines in the sub scanning direction, complicating circuit configuration.
The present invention provides a split scanning optical apparatus that can perform correction of a positional deviation of split scanning lines in the sub scanning direction and modification of image information split positions with a simple circuit configuration.
The split scanning optical apparatus according to the present invention has plural split scanning units for performing scanning within split areas split in a main scanning area and performs exposure for one-time main scanning by performing scanning at the same time by the plural split scanning units. The split scanning optical apparatus also has an image information split part that is provided with overlap areas in scanning areas of the split scanning units, an identical portion on a surface to be scanned being exposable mutually in the overlap areas, and splits image information to be provided by exposure to a surface to be scanned into split image information to be provided respectively by the split scanning units. The apparatus further has plural storage parts that respectively store the split image information, plural address specification units that respectively specify storage addresses to the storage parts, and a store operation control unit that controls a store operation of the storage parts so that a split position of the image information falls in an overlapping range of plural storage parts specified by the address specification parts.
According to this apparatus, the address specification part can specify storage addresses to the storage parts so that mutually adjacent pieces of split image information can be stored in an overlapped form, whereby image information is split within a range of addresses of the overlap area by the store operation control part. Therefore, a split position can be freely selected.
The apparatus may further have a timing change part that changes split timing by the store operation control part for every main scanning operation or for every certain plural number of main scanning operations.
According to this apparatus, with a finished image in mind, the finished image would be made finer by obliquely or randomly connecting split positions of main scanning than straightly from top to bottom connecting them. Accordingly, the quality of a finished image can be improved by changing the switching timing of the store operation switching part for every main scanning operation or for every certain plural number of main scanning operations.
In the split scanning optical apparatus, the store operation control part may function as an image information disabling part that outputs a dummy signal as a light source off signal to addresses within the range of the overlap area specified by the address specification parts in storage parts other than storage parts that store image information.
According to this apparatus, in storage parts other than storage parts that store image information, dummy signals are stored in addresses within the range of an overlap area. Accordingly, a split position in the column direction, that is, the main scanning direction can be freely changed by inserting the dummy signals, and furthermore, a split position can be changed on a one-line basis based on the number of dummy signals.
In view of control, a split is considered to always have taken place at an identical position. Therefore, a deviation in the row direction, that is, the sub scanning direction need not be subjected to feedback control, so that only a deviation amount may be compensated.
In the split scanning optical apparatus, if image information corresponding to the dummy signal is detected before the information split takes place, an image split store operation by the image information disabling part may be performed upon detecting the image information corresponding to the dummy signal.
According to this apparatus, when a split position is selected, if there exists information for which a light source does not go on, that is, image information for which the output of a laser beam goes off when an image is formed by the laser beam, selection of the position as a split position helps to minimize reduction in image quality by split scanning.
In the split scanning optical apparatus, the store operation control part may function as a store operation switching part that, when both two address specification parts are busy, cancels a store operation on split image information A to a storage part thereof and switches to a store operation on split image information B to a storage part thereof, wherein the two pieces A and B of split image information each contain identical image information in the overlap area and one of the address specification parts controls a store operation on the split image information A to the storage part thereof and the other controls a store operation on the split image information B to the storage part thereof.
According to this apparatus, identical information in the overlap area can be stored in both the split image information A and the split image information B. If there are two or more split positions, two mutually adjacent pieces of split image information may be considered individually.
At least, for image information in the overlap area, the operation of the respective address specification parts to control a store operation to the respective storage parts of the split image information pieces A and B is started and the two storage parts are allocated areas capable of storing the image information of the overlap area.
Accordingly, if both two address specification parts are busy, at any time, a store operation on the split image information A to the storage part can be canceled to switch to a store operation on the split image information B to the storage part.
In the store operation switching part, no time priority is Bet between the function to cancel a store operation on the split image information A to the storage part and the function to switch to a store operation on the split image information B to the storage part.